Manufacture of group iiia-nitride layers on semiconductor on insulator structures

ABSTRACT

A method is provided for forming Group IIIA-nitride layers, such as GaN, on substrates. The Group IIIA-nitride layers may be deposited on mesa-patterned semiconductor-on-insulator (SOI, e.g., silicon-on-insulator) substrates. The Group IIIA-nitride layers may be deposited by heteroepitaxial deposition on mesa-patterned semiconductor-on-insulator (SOI, e.g., silicon-on-insulator) substrates.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 15/538,474, which was filed Jun. 21, 2017, the entire disclosure ofwhich is hereby incorporated by reference in its entirety. U.S.application Ser. No. 15/538,474 is a 35 U.S.C. § 371 National StageApplication of International Application No. PCT/US2015/067139, whichwas filed Dec. 21, 2015, the entire disclosure of which is herebyincorporated by reference in its entirety. International Application No.PCT/US2015/067139 claims priority to U.S. Provisional Patent ApplicationNo. 62/095,282 filed on 22 Dec. 2014, the entire disclosure of which ishereby incorporated by reference in its entirety.

THE FIELD OF THE INVENTION

The present invention generally relates to the field of semiconductorwafer manufacture. More specifically, the present invention relates to amethod for forming a Group IIIA-nitride layer on the device layer of asemiconductor-on-insulator (e.g., silicon-on-insulator) structure.

BACKGROUND OF THE INVENTION

Semiconductor wafers are generally prepared from a single crystal ingot(e.g., a silicon ingot) which is trimmed and ground to have one or moreflats or notches for proper orientation of the wafer in subsequentprocedures. The ingot is then sliced into individual wafers. Whilereference will be made herein to semiconductor wafers constructed fromsilicon, other materials may be used to prepare semiconductor wafers,such as silicon carbide, sapphire, and aluminum nitride.

Semiconductor wafers (e.g., silicon wafers) may be utilized in thepreparation of composite layer structures. A composite layer structure(e.g., a semiconductor-on-insulator, and more specifically, asilicon-on-insulator (SOI) structure) generally comprises a handle waferor layer, a device layer, and an insulating (i.e., dielectric) film(typically an oxide layer) between the handle layer and the devicelayer. Generally, the device layer is between 0.01 and 20 micrometersthick, such as between 0.05 and 20 micrometers thick. In general,composite layer structures, such as silicon-on-insulator (SOI),silicon-on-sapphire (SOS), and silicon-on-quartz, are produced byplacing two wafers in intimate contact, followed by a thermal treatmentto strengthen the bond.

After thermal anneal, the bonded structure undergoes further processingto remove a substantial portion of the donor wafer to achieve layertransfer. For example, wafer thinning techniques, e.g., etching orgrinding, may be used, often referred to as back etch SOI (i.e., BESOI),wherein a silicon wafer is bound to the handle wafer and then slowlyetched away until only a thin layer of silicon on the handle waferremains. See, e.g., U.S. Pat. No. 5,189,500, the disclosure of which isincorporated herein by reference as if set forth in its entirety. Thismethod is time-consuming and costly, wastes one of the substrates andgenerally does not have suitable thickness uniformity for layers thinnerthan a few microns.

Another common method of achieving layer transfer utilizes a hydrogenimplant followed by thermally induced layer splitting. Particles (e.g.,hydrogen atoms or a combination of hydrogen and helium atoms) areimplanted at a specified depth beneath the front surface of the donorwafer. The implanted particles form a cleave plane in the donor wafer atthe specified depth at which they were implanted. The surface of thedonor wafer is cleaned to remove organic compounds deposited on thewafer during the implantation process.

The front surface of the donor wafer is then bonded to a handle wafer toform a bonded wafer through a hydrophilic bonding process. Prior tobonding, the donor wafer and/or handle wafer are activated by exposingthe surfaces of the wafers to plasma containing, for example, oxygen ornitrogen. Exposure to the plasma modifies the structure of the surfacesin a process often referred to as surface activation, which activationprocess renders the surfaces of one or both of the donor water andhandle wafer hydrophilic. The wafers are then pressed together, and abond is formed there between. This bond is relatively weak, and must bestrengthened before further processing can occur.

In some processes, the hydrophilic bond between the donor wafer andhandle wafer (i.e., a bonded wafer) is strengthened by heating orannealing the bonded wafer pair. In some processes, wafer bonding mayoccur at low temperatures, such as between approximately 300° C. and500° C. In some processes, wafer bonding may occur at high temperatures,such as between approximately 800° C. and 1100° C. The elevatedtemperatures cause the formation of covalent bonds between the adjoiningsurfaces of the donor wafer and the handle wafer, thus solidifying thebond between the donor wafer and the handle wafer. Concurrently with theheating or annealing of the bonded wafer, the particles earlierimplanted in the donor wafer weaken the cleave plane.

A portion of the donor wafer is then separated (i.e., cleaved) along thecleave plane from the bonded wafer to form the SOI wafer. Cleaving maybe carried out by placing the bonded wafer in a fixture in whichmechanical force is applied perpendicular to the opposing sides of thebonded wafer in order to pull a portion of the donor wafer apart fromthe bonded wafer. According to some methods, suction cups are utilizedto apply the mechanical force. The separation of the portion of thedonor wafer is initiated by applying a mechanical wedge at the edge ofthe bonded wafer at the cleave plane in order to initiate propagation ofa crack along the cleave plane. The mechanical force applied by thesuction cups then pulls the portion of the donor wafer from the bondedwafer, thus forming an SOI wafer.

According to other methods, the bonded pair may instead be subjected toan elevated temperature over a period of time to separate the portion ofthe donor wafer from the bonded wafer. Exposure to the elevatedtemperature causes initiation and propagation of a crack along thecleave plane, thus separating a portion of the donor wafer. This methodallows for better uniformity of the transferred layer and allows recycleof the donor wafer, but typically requires heating the implanted andbonded pair to temperatures approaching 500° C.

Crystal growth of bulk Group IIIA-nitrides, particularly GaN, ischallenging and has not been successful in volume production.Conventionally, Group IIIA-nitrides, such as GaN, are produced byheteroepitaxial deposition on wafer substrates made of sapphire, siliconcarbide, and silicon. Deposition of Group IIIA-nitrides on semiconductorwafers is challenging due to mismatch of the coefficient of thermalexpansion (CTE) between GaN and the substrate, which leads to large bowof the wafer substrate and cracks in the deposited Group IIIA-nitridelayer.

Conventionally, there have been several engineering approaches toaddress the residual stress in heteroepitaxially deposited GroupIIIA-nitride, e.g., GaN, layers on semiconductor substrates. In onesolution, Group IIIA-nitride layers are deposited on thick semiconductorsubstrates. For example, silicon substrates have been used having athickness of at least about 1.0 millimeter, such as 1.5 millimeters havebeen used to reduce the wafer bow caused by the heteroepitaxiallydeposited GaN layer. This approach does not change the stress, but doesmitigate stress induced substrate deformation by increasing thestiffness of the substrate. Although the wafer bow is reduced, theresidual stress does not change and cracks in the GaN layer may still bepresent. Cracks are a killer defect for the growth of thick GaN layers(>5 um) as used in high-voltage power devices (>800V). Layer crackingand wafer bow become more severe when scaling the substrate diameter upto 200 mm or beyond.

In another technique for reducing defectivity in the deposited GroupIIIA-nitride layer (e.g., GaN), a buffer layer having a thicknessbetween about 2 micrometers and about 5 micrometers may be deposited onthe wafer substrate prior to formation of the Group IIIA-nitride layer(e.g., GaN). The buffer layer may comprise aluminum nitride, aluminumgallium nitride, or a multilayer comprising aluminum nitride andaluminum gallium nitride. The residual stress in the AlN/AlGaN bufferstends to deform the substrate and thus creates temperaturenon-uniformity across the substrate, which results in non-uniformity ineither layer thickness or composition. See Dadgar, Journal of CrystalGrowth, 272 (2004) 72-75. Additionally, stress in the GaN layer raises aconcern in terms of device performance. See Zhang, J. Appl. Phys., 108,073522 (2010).

In another approach, the buffer structure is optimized to inducecompressive stress in the Group IIIA-nitride layer (e.g., GaN) so thatthe CTE mismatch induced tensile stress can be partially compensated. Anexample of this technique is the use of a thin low-temperature AlNinterlayer during GaN epitaxial growth. GaN grown on strain relaxed AlNor AlGaN layer is compressively stressed. As the dislocation in GaN haslow mobility, the strain relaxation in GaN layer is not complete. At theend of epitaxy, a compressive stress is left in the GaN layer tocompensate the tensile stress induced by CTE mismatch. See, e.g., Amano,J. Appl. Phys. 37, L1540 (1998), and Krost & Dadgar, Phys. Stat. Sol.(a) 200, No. 1, 26-35 (2003). As the AlN interlayer and the AlGaN bufferlayer only partially compensate the tensile stress in GaN, thecrack-free GaN thickness is still limited to a few micrometers.

In yet another approach, Group IIIA-nitrides, such as GaN, are grown onpatterned substrates. See, e.g., U.S. Pat. No. 8,507,737, whichdiscloses GaN growth on patterned sapphire substrates. See also U.S.Pub. No. 2011/004568, which discloses grooved substrates. It has alsobeen reported that GaN may grow on patterned Si (111) substrates. SeeKawaguch, phys. stat. sol. (a) 176, 553 and Sawaki, Journal of CrystalGrowth 311 (2009) 2867-2874. The aim of this method is to relieve thestress at the edge of the GaN islands. However, the stress relief isonly effective in GaN layers with lateral dimension of a few hundredmicrometers.

Still further, GaN has been grown on compliant substrates. GaN growth onSOI substrates shows improved crystalline quality as discussed by Cao,J. Appl. Phys., 83, 3829, 1998. However, there is no detailed study onthe advantage of using blanket SOI substrates in terms of crack andstress relaxation. This approach may reduce GaN defectivity but notnecessarily increase the thickness of crack-free GaN.

Finally, the use of a backside CTE layer to balance wafer bow has beendisclosed in U.S. Pub. No. 2012/0132921. U.S. Pub. No. 2012/0132921discloses a method to balance the tensile stress in GaN using a CTElayer on the backside of the substrate. The challenge of this method isthat the response of the CTE film to temperature change must follow thatof GaN.

SUMMARY OF THE INVENTION

A method is provided for depositing Group IIIA-nitride layers onsemiconductor-on-insulator (SOI) substrates. In some embodiments, GroupIIIA-nitride layers (e.g., gallium nitride (GaN) layers) are formed byheteroepitaxial deposition on semiconductor-on-insulator substrates.Prior to deposition of the Group IIIA-nitride layers, thesemiconductor-on-insulator substrates are subjected to a process thatyields a pattern of mesa islands in the device layer of the SOIsubstrate. In some embodiments, the pattern of mesa islands comprisessemi-floating, floating, or combinations of both floating andsemi-floating mesa islands supported by supporting columns formed in thedielectric layer of the SOI substrates. The Group IIIA-nitride layersmay be formed on the mesa islands formed in the device layers. Thismethod is designed to address the mismatch of coefficients of thermalexpansion (CTE) between a Group IIIA-nitride, e.g., GaN, and thesubstrate as well as to provide Group IIIA-nitride epitaxial templatesthat are ready to be transferred to a dissimilar carrier substrate atlow cost.

Briefly, the present invention is directed to a method of forming amultilayer structure. The method comprises: forming a pattern comprisinga plurality of mesa islands on a semiconductor-on-insulator structure,wherein the semiconductor-on-insulator structure comprises a singlecrystal semiconductor handle wafer, a dielectric layer in interfacialcontact with the single crystal semiconductor handle wafer, and a singlecrystal semiconductor device layer in interfacial contact with thedielectric layer, and further wherein the pattern comprising theplurality of mesa islands is formed in the single crystal semiconductordevice layer; and forming a Group IIIA-nitride layer on the plurality ofmesa islands.

The present invention is further directed to a multilayer structurecomprising: a single crystal semiconductor handle wafer comprising twomajor, generally parallel surfaces, one of which is a front surface ofthe single crystal semiconductor handle wafer and the other of which isa back surface of the single crystal semiconductor handle wafer, acircumferential edge joining the front and back surfaces of the singlecrystal semiconductor handle wafer, a bulk region between the front andback surfaces, and a central plane of the single crystal semiconductorhandle wafer between the front and back surfaces of the single crystalsemiconductor handle wafer; a dielectric layer in interfacial contactwith a major surface of the single crystal semiconductor handle wafer; asingle crystal semiconductor device layer in interfacial contact withthe dielectric layer, the single crystal semiconductor device layercomprising a pattern comprising a plurality of mesa islands; and a GroupIIIA-nitride layer on the mesa islands.

The present invention is still further directed to a multilayerstructure comprising: a carrier substrate; an interfacial bonding layer;and a Group IIIA-nitride layer, the Group IIIA-nitride layer having athickness between about 500 nanometers and about 1000 micrometers.

Other objects and features of this invention will be in part apparentand in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1D depict an embodiment of the process of the presentinvention.

FIG. 2A depicts a pattern of semi-floating mesa islands on an SOIsubstrate according to an embodiment of the present invention.

FIG. 2B depicts a pattern of floating mesa islands on an SOI substrateaccording to an embodiment of the present invention.

FIG. 3A depicts a multilayer structure according to an embodiment of thepresent invention. In one embodiment, the multilayer structure depictedin FIG. 3A comprises a light emitting diode (LED) device formed directlyon a Group IIIA-nitride on mesa islands.

FIG. 3B depicts a multilayer structure according to an embodiment of thepresent invention. In one embodiment, the multilayer structure depictedin FIG. 3B comprises a high-electron-mobility transistor (HEMT) powerdevice formed directly on a Group IIIA-nitride on mesa islands.

FIG. 4 is a depiction of a lateral high-electron-mobility transistor(HEMT) power device that may be built on a Group IIIA-nitride layer onmesa islands.

FIGS. 5A through 5D depict an embodiment of the process of the presentinvention.

DETAILED DESCRIPTION OF THE EMBODIMENT(S) OF THE INVENTION

According to the present invention, a method is provided for forming aGroup IIIA-nitride layer, such as a layer comprising GaN, on asubstrate. In some embodiments, the Group IIIA-nitride layer (e.g., aGaN layer) is deposited on a mesa-patterned semiconductor-on-insulator(SOI, e.g., silicon-on-insulator) substrate. In some embodiments, theGroup IIIA-nitride layer may be deposited by heteroepitaxial depositionon mesa-patterned semiconductor-on-insulator (SOI, e.g.,silicon-on-insulator) substrates. More particularly, asemiconductor-on-insulator structure is prepared to comprise a patterncomprising a plurality of mesa islands. The pattern comprising theplurality of mesa islands is formed in the single crystal semiconductordevice layer (e.g., a single crystal silicon device layer) of the SOIsubstrate. In the context of the present disclosure, reference to“device layer” is to the layer of semiconductor material (typicallysingle crystal silicon) on an SOI substrate that results from aconventional layer transfer process used to form a SOI structure. Statedanother way, an SOI structure comprises a handle wafer, a dielectriclayer (typically a buried oxide layer, or BOX), and a device layer, andit is formed by conventional layer transfer using a handle wafer and adonor wafer. The device layer is derived from a single crystalsemiconductor donor wafer. A “device layer” in the context of thisdisclosure does not necessarily refer to the semiconductor material inwhich a device may be formed. Rather, in the context of this disclosure,devices are generally formed in the Group IIIA-nitride layers formed bythe method of the present invention. The Group IIIA-nitride layer may beformed on the mesa islands formed in the single crystal semiconductordevice layer of an SOI substrate.

In some embodiments, a buffer layer may be formed on the plurality ofmesa islands formed in the single crystal semiconductor device layer.The Group IIIA-nitride layer may be formed on the buffer layer formed onthe mesa islands. In the context of the present invention, a mesa islandformed in the single crystal semiconductor device layer (e.g., a singlecrystal silicon device layer) comprises a flat surface for deposition ofa Group IIIA-nitride. Essentially perpendicular to the depositionsurface are sidewalls that define the contours of the mesa islands. Themesa islands are supported by the dielectric layer of thesemiconductor-on-insulator structure.

In some embodiments, the dielectric layer is modified by removing aportion thereof, leaving support columns underneath the mesa islands. Insome embodiments, therefore, the pattern of semi-floating, floating, orcombinations of floating and semi-floating single crystal semiconductormesa islands is supported by the supporting columns derived from thedielectric layer. In the context of the present invention, a pattern ofsemi-floating islands comprises interconnection or bridging betweenislands. See, e.g., FIG. 2A. Interconnecting the islands withsemiconductor material derived from the device layer helps overcomegravity induced layer collapse. In some embodiments, e.g., FIG. 2B, themesa islands are floating in that the islands lack an interconnectingbridge between islands. In still further embodiments, the pattern ofmesa islands may comprise both floating and semi-floating islands, i.e.,in some segments of the wafer, the mesa islands may be connected bysemiconductor material, while in other segments of the wafer, the mesaislands are not connected. The method of the present invention isintended to address the mismatch of coefficients of thermal expansion(CTE) between GaN and the SOI substrate.

In some embodiments, devices may be manufactured directly in the GroupIIIA-nitride layer formed on the pattern of mesa islands. In someembodiments, the Group IIIA-nitride layer grown on the patterncomprising a plurality of mesa islands may be transferred to adissimilar carrier substrate, and the Group IIIA-nitride layer mayundergo further growth prior to manufacture of devices in the GroupIIIA-nitride layer. In some embodiments, GaN templates grown on the SOIstructure are ready to be transferred to a dissimilar carrier substrate.The method enables the transfer of a Group IIIA-nitride layer to adissimilar carrier substrate at low cost. In some embodiments, after theGroup IIIA-nitride layer is transferred to the dissimilar carriersubstrate, it may be thickened. In some embodiments, the thickeningtechnique comprises epitaxial deposition. Devices may be fabricated inthe thickened Group IIIA-nitride layer. In some embodiments, the methodof the present invention enables manufacture of devices that cancurrently be made only on bulk GaN such as vertical GaN on GaN highvoltage power device, GaN on GaN LEDs, and laser diodes.

1. Semiconductor-On-Insulator Substrate

The substrates for use in the present invention aresemiconductor-on-insulator structures, e.g., a silicon-on-insulatorstructure. See FIG. 1A. A semiconductor-on-insulator structure 10 isformed by bonding a semiconductor handle wafer 12 and a semiconductordonor wafer. A dielectric layer 14 is located between the semiconductorhandle wafer 12 and the semiconductor device layer 16. During SOImanufacture, the intervening dielectric layer 14 may be formed on thefront surface of the semiconductor handle wafer 12, or it may be formedon the semiconductor donor wafer. In some SOI manufacture processes,dielectric layers may be formed on both wafers. The semiconductor devicelayer 16 in a semiconductor-on-insulator composite structure 10 isderived from a semiconductor donor wafer. The semiconductor device layer16 may be transferred onto the semiconductor handle wafer 12 by waferthinning techniques such as etching a semiconductor donor substrate orby cleaving a semiconductor donor substrate comprising a damage plane.

In general, the single crystal semiconductor handle wafer 12 and singlecrystal semiconductor donor wafer (the device layer 16 is derived fromthe donor wafer in SOI manufacture) comprise two major, generallyparallel surfaces. One of the parallel surfaces is a front surface ofthe wafer, and the other parallel surface is a back surface of thewafer. Wafers comprise a circumferential edge joining the front and backsurfaces, and a central plane between the front and back surfaces.Wafers additionally comprise an imaginary central axis perpendicular tothe central plane and a radial length that extends from the central axisto the circumferential edge. In addition, because wafers, e.g., siliconwafers, typically have some total thickness variation (TTV), warp, andbow, the midpoint between every point on the front surface and everypoint on the back surface may not precisely fall within a plane. As apractical matter, however, the TTV, warp, and bow are typically soslight that to a close approximation the midpoints can be said to fallwithin an imaginary central plane which is approximately equidistantbetween the front and back surfaces.

With reference still to FIG. 1A, the semiconductor device layer 16 in asemiconductor-on-insulator composite structure 10 is derived from asingle crystal semiconductor donor wafer. The semiconductor device layer16 may be transferred onto the semiconductor handle wafer 12 by waferthinning techniques such as etching a semiconductor donor substrate orby cleaving a semiconductor donor substrate comprising a damage plane.Upon completion of conventional bonding and wafer thinning steps, thesemiconductor-on-insulator (e.g., silicon-on-insulator) compositestructure 10 comprises the single crystal semiconductor handle wafer 12,a dielectric layer 14 such as a buried oxide layer, and the singlecrystal semiconductor device layer 16. A finished SOI substrate issubjected to mesa patterning according to the method of the presentinvention, prior to deposition of the Group IIIA-nitride layer. Morespecifically, the device layer 16 is subjected to a series of steps tothereby form a pattern of mesa islands in the semiconductor devicelayer. See FIG. 1B, in which a semiconductor-on-insulator (e.g.,silicon-on-insulator) composite structure 10 comprising a single crystalsemiconductor handle wafer 12, a dielectric layer 14 such as a buriedoxide layer, and a pattern of mesa islands 18, which are derived fromthe semiconductor device layer 16 of FIG. 1A. It is upon this pattern ofmesa islands 18 (FIGS. 1B and 1C) formed from the device layer 16 (FIG.1A) that the Group IIIA-nitride layers are formed. In some embodiments,the pattern of mesa islands 18 may comprise semi-floating islands. SeeFIG. 2A, which is top view exemplary depiction of semi-floating mesaislands. In the context of the present invention, a pattern ofsemi-floating islands comprises interconnection or bridging betweenislands. This is represented by the semiconductor material linkingislands in FIG. 2A, which is a top view of a pattern of interconnectedmesa islands. The bridging semiconductor material, which is derived fromthe device layer 16 of FIG. 1A may be substantially located as depictedin FIG. 2A, but other linking configurations are possible, such assubstantially connecting at or near the middle of the islands, andfurther one island may be linked with one adjacent island, two adjacentislands, three adjacent islands, four adjacent islands, or even moredepending up on the shape of the islands. In some embodiments, thepattern of mesa islands 18 may comprise floating islands. See FIG. 2B,which is top view depiction of floating mesa islands. As depicted inFIG. 2B, the mesa islands are floating in that the islands lack aninterconnecting bridge between islands. In yet other embodiments, thepattern of mesa islands may comprise both floating and semi-floatingislands, i.e., in some segments of the wafer, the mesa islands may beconnected by semiconductor material, while in other segments of thewafer, the mesa islands are not connected. Still further, the dielectriclayer may also be etched to reveal supporting columns that support themesa islands. See FIG. 1C, which depicts the semiconductor-on-insulator(e.g., silicon-on-insulator) composite structure 10 comprising thesingle crystal semiconductor handle wafer 12 and the pattern of mesaislands 18. The SOI structure 10 of FIG. 1C comprises support structures20 underneath each mesa island. The support structures 20 comprise adielectric material (e.g., silicon dioxide) since they are derived fromthe dielectric layer 14 as depicted in FIGS. 1A and 1B.

The semiconductor handle wafer 12 and the device layer 16 may comprisesingle crystal semiconductor material. In some embodiments, thesemiconductor material may be selected from the group consisting ofsilicon, silicon carbide, sapphire, and aluminum nitride. In someembodiments, the semiconductor may comprise silicon or sapphire. Thehandle wafer 12 and the device layer 14 may comprise the samesemiconductor material, or they may be different. In view thereof, SOIstructures 16 may comprise, e.g., silicon-on-insulator,sapphire-on-insulator, aluminum nitride-on-insulator, and othercombinations. The semiconductor-on-insulator structures 16 typicallyhave a nominal diameter of at least about 150 mm, at least about 200 mm,at least about 300 mm, or at least about 450 mm. Thicknesses may varyfrom about 250 micrometers to about 1500 micrometers, such as betweenabout 300 micrometers and about 1000 micrometers, suitably within therange of about 500 micrometers to about 1000 micrometers.

In particularly preferred embodiments, the semiconductor on insulatorstructures 10 are prepared from handle wafers and donor wafers that aresingle crystal silicon wafers which have been sliced from a singlecrystal ingot grown in accordance with conventional Czochralski crystalgrowing methods or float zone growing methods. Such methods, as well asstandard silicon slicing, lapping, etching, and polishing techniques aredisclosed, for example, in F. Shimura, Semiconductor Silicon CrystalTechnology, Academic Press, 1989, and Silicon Chemical Etching, (J.Grabmaier ed.) Springer-Verlag, N.Y., 1982 (incorporated herein byreference). Preferably, the wafers are polished and cleaned by standardmethods known to those skilled in the art. See, for example, W. C.O'Mara et al., Handbook of Semiconductor Silicon Technology, NoyesPublications. If desired, the wafers can be cleaned, for example, in astandard SC1/SC2 solution. In some embodiments, the single crystalsilicon wafers of the present invention are single crystal siliconwafers which have been sliced from a single crystal ingot grown inaccordance with conventional Czochralski (“Cz”) crystal growing methods,typically having a nominal diameter of at least about 150 mm, at leastabout 200 mm, at least about 300 mm, or at least about 450 mm.Preferably, both the single crystal silicon handle wafer and the singlecrystal silicon donor wafer have mirror-polished front surface finishesthat are free from surface defects, such as scratches, large particles,etc. Wafer thickness may vary from about 250 micrometers to about 1500micrometers, such as between about 300 micrometers and about 1000micrometers, suitably within the range of about 500 micrometers to about1000 micrometers. In some specific embodiments, the wafer thickness maybe about 725 micrometers.

In some embodiments, the single crystal semiconductor wafers, i.e.,handle wafer and donor wafer, comprise interstitial oxygen inconcentrations that are generally achieved by the Czochralski-growthmethod. In some embodiments, the semiconductor wafers comprise oxygen ina concentration between about 4 PPMA and about 18 PPMA. In someembodiments, the semiconductor wafers comprise oxygen in a concentrationbetween about 10 PPMA and about 35 PPMA. In some embodiments, the singlecrystal silicon handle wafer comprises oxygen in a concentration of nogreater than about 10 PPMA. Interstitial oxygen may be measuredaccording to SEMI MF 1188-1105.

The single crystal silicon handle wafer 12 may have any of (100), (110),or (111) crystal orientation. The crystal orientation of the handlewafer 12 is often not critical since the handle wafer 12 is often not apart of the finished device. In some embodiments, the single crystalsilicon donor wafer has a (111) crystal orientation. Accordingly andagain with reference to FIG. 1A, the semiconductor-on-insulatorstructure 10 comprises a single crystal device layer 14 having a (111)crystal orientation. The (111) silicon crystal orientation is preferredin order to obtain high quality epitaxial growth of Group IIIA-nitridematerials. Other crystal orientations, such as (100) and (110), are notas successful for epitaxial deposition of Group IIIA-nitrides. Forexample, the (111) silicon crystal orientation is preferred since it isconsistent with the hexagonal growth habit of GaN.

In some embodiments, the single crystal semiconductor handle wafer 12,such as a single crystal silicon handle wafer, and/or the semiconductordevice layer 16, e.g., a single crystal silicon device layer, has arelatively high minimum bulk resistivity. High resistivity wafers aregenerally sliced from single crystal ingots grown by the Czochralskimethod or float zone method. Cz-grown silicon wafers may be subjected toa thermal anneal at a temperature ranging from about 600° C. to about1000° C. in order to annihilate thermal donors caused by oxygen that areincorporated during crystal growth. In some embodiments, the singlecrystal semiconductor handle wafer has a minimum bulk resistivity of atleast 10 Ohm-cm, at least 100 Ohm-cm, at least about 500 Ohm-cm, atleast about 1000 Ohm-cm, or even at least about 3000 Ohm-cm, such asbetween about 100 Ohm-cm and about 100,000 Ohm-cm, or between about 500Ohm-cm and about 100,000 Ohm-cm, or between about 1000 Ohm-cm and about100,000 Ohm-cm, or between about 500 Ohm-cm and about 10,000 Ohm-cm, orbetween about 750 Ohm-cm and about 10,000 Ohm-cm, between about 1000Ohm-cm and about 10,000 Ohm-cm, between about 2000 Ohm-cm and about10,000 Ohm-cm, between about 3000 Ohm-cm and about 10,000 Ohm-cm, orbetween about 3000 Ohm cm and about 5,000 Ohm-cm. Methods for preparinghigh resistivity wafers are known in the art, and such high resistivitywafers may be obtained from commercial suppliers, such as SunEdisonSemiconductor Ltd. (St. Peters, Mo.; formerly MEMC Electronic Materials,Inc.).

To form the semiconductor-on-insulator structure 10, the single crystalsemiconductor handle wafer 12 is bonded to a single crystalsemiconductor donor wafer, e.g., a single crystal semiconductor donorwafer, which is prepared according to conventional layer transfermethods. That is, the single crystal semiconductor donor wafer may besubjected to standard process steps including oxidation, implant, andpost implant cleaning. Accordingly, a single crystal semiconductor donorwafer of a material that is conventionally used in preparation ofmultilayer semiconductor structures, e.g., a single crystal silicondonor wafer, that has been etched and polished and oxidized, issubjected to ion implantation to form a damage layer in the donorsubstrate.

The handle wafer and donor wafer are brought into intimate contact tothereby form a bonded structure. Since the mechanical bond is relativelyweak, the bonded structure is further annealed by conventional methodsto solidify the bond between the donor wafer and the handle wafer. Afterthe thermal anneal, the bond between the wafers is strong enough toinitiate layer transfer via cleaving the bonded structure at the cleaveplane. Cleaving may occur according to techniques known in the art. Withreference to FIG. 1A, cleaving removes a portion of the semiconductordonor wafer, thereby leaving a semiconductor device layer 16, preferablya silicon device layer, in interfacial contact with a dielectric layer14 (i.e., a buried oxide layer or BOX), which is in contact with asingle crystal semiconductor (e.g., silicon) handle wafer 12. The entirestructure comprises the semiconductor-on-insulator composite structure10, which is the substrate for the process of the present invention.

With reference again to FIG. 1A, between the handle substrate 12 and thedevice layer 16 is a dielectric layer 14. Suitable dielectric layer 14materials include silicon dioxide, silicon nitride, silicon oxynitride,hafnium oxide, titanium oxide, zirconium oxide, lanthanum oxide, bariumoxide, and a combination thereof. In some preferred embodiments, thedielectric layer 14 comprises a buried oxide layer, i.e., a BOX. Thedielectric layer thickness may be between about 10 nanometers and about5000 nanometers, such as between about 10 nanometers and about 1000nanometers, such as between about 50 nanometers and about 500nanometers.

The single crystal semiconductor device layer 16, e.g., a single crystalsilicon device layer, may have a thickness between about 1 nanometer andabout 500 nanometers, such as between about 5 nanometers and about 100nanometers. Again, the SOI structure 10 preferably comprises a devicelayer 16 having Si (111) crystal orientation in order to obtain highquality epitaxial growth of Group IIIA-nitride materials.

2. Forming Mesa Islands in the Device Layer of aSemiconductor-On-Insulator Substrate

According to the method of the present invention, and with reference toFIG. 1B, a pattern comprising a plurality of mesa islands 18 is formedon a semiconductor-on-insulator structure 10. More specifically, thepattern comprising the plurality of mesa islands 18 is formed in thesingle crystal semiconductor device layer 16. Compare FIG. 1A and FIG.1B, which are illustrations depicting the starting SOI substrate (FIG.1A) and an SOI substrate comprising a pattern of mesa islands 18 (FIG.1B), in which the mesa islands are prepared in the originalsemiconductor device layer 16. The pattern comprising the plurality ofmesa islands 18 preferably comprises shapes formed into thesemiconductor device layer 16 that are useful in the final structurewhich incorporates the Group IIIA-nitride layer. In some embodiments,the mesa islands 18 are formed by removing a portion of the singlecrystal semiconductor device layer 16. In some embodiments, the mesaislands 18 are formed using lithography. Lithography defines thepatterns by photoresist. The removal of the semiconductor material inthe device layer 16, e.g., silicon between islands, is realized byselective etch of semiconductor material, e.g., silicon using reactiveion etch (RIE) or wet etch. In RIE, Cl₂ gas selectively etchessemiconductor, e.g., silicon. In wet etch, an aqueous KOH solution or anaqueous TMAH solution can be used. Once the device layer 16 is opened,the photoresist is stripped and the wafer is subject to HF solution tounder etch the BOX so that floating and semi-floating mesa islands 18(FIG. 1C) are obtained. The shape of the islands is not critical, butrectangular or square shapes are preferred for device fabrication on theGaN layers. See FIG. 2A depicting a pattern of semi-floating mesaislands on an SOI substrate according to an embodiment of the presentinvention, and FIG. 2B depicting a pattern of floating mesa islands onan SOI substrate according to an embodiment of the present invention.

In some embodiments of the mesa patterning, floating mesa islands, i.e.,mesa islands with no interconnecting bridges of semiconductor material,are not preferred because it is preferable to maximize the lateraldimension of the islands. Moreover, interconnection or bridging betweenislands helps overcome gravity induced layer collapse. In some preferredembodiments, the portion of the single crystal semiconductor devicelayer 16 removed to form a pattern of mesa islands 18 in the singlecrystal semiconductor device layer leaves a pattern in which each mesaisland has a quadrilateral shape, e.g., square, rectangle, rhombus,parallelogram, etc., when viewed from the top. See, e.g., FIGS. 2A and2B for depictions of an exemplary suitable mesa island shape. In someembodiments, each side of the quadrilateral shape has a dimensionbetween about 10 micrometers and about 10,000 micrometer. The dimensionsof the mesa islands may depend upon the die size required for thedesired end use. For example, power device die sizes may range fromabout 1000 micrometers to about 10,000 micrometers. Die sizes for LEDdevices may range from about 10 micrometers to about 1000 micrometers,such as between about 10 micrometers and about 500 micrometers.Moreover, in some embodiments, the mesa islands may be separated by agap having a distance between about 1 micrometer and about 100micrometers.

In some embodiments, the portion of the single crystal semiconductordevice layer 16 (FIG. 1A) removed to form a pattern of mesa islands 18(FIGS. 1B and 1C) in the single crystal semiconductor device layerleaves a pattern in which each mesa island has a rectangular shape, whenviewed from the top. See, e.g., FIGS. 2A and 2B, which are top views ofSOI structure in which a portion of the donor layer is removed to form apattern comprising a plurality of rectangular mesa islands. In someembodiments, the portion of the single crystal semiconductor devicelayer 16 (FIG. 1A) removed to form a pattern of mesa islands 18 (FIGS.1B and 1C) in the single crystal semiconductor device layer leaves apattern in which each mesa island has a square shape, when viewed fromthe top. In some embodiments, each side of the rectangular or squareshape has a dimension between about 10 micrometers and about 10,000micrometer. Moreover, in some embodiments, the mesa islands areseparated by a gap having a distance between about 1 micrometer andabout 100 micrometers.

After removing a portion of the single crystal semiconductor devicelayer 16 to reveal a pattern of mesa islands 18 (e.g., rectangularislands on the buried oxide layer) in the device layer as depicted inFIG. 1B (and exemplified in FIGS. 2A and 2B), in some embodiments of theinvention, the SOI substrate 10 is etched to remove a portion of thedielectric layer 14 to thereby form a layer of support structures 20underneath the mesa islands 18. See FIG. 1C for an exemplary,non-limiting depiction of support structures 20 supporting a pattern ofmesa islands 18. In some embodiments, a dielectric layer 14, e.g.,silicon dioxide, is partially removed so that a pattern of semi-floatingor floating or both single crystal silicon mesa islands 18 is obtained.See FIG. 1C. The dielectric layer 14, e.g., the BOX, may be etched usinghydrofluoric acid, either aqueous or vapor. In one embodiment, thedielectric layer 14 may be etched using an HF solution (0.5-10%) in awet bench. In one embodiment, the dielectric layer 14 may be etchedusing HF vapor in a closed chamber. In some embodiments, the dielectriclayer 14 is etched so that the remaining support columns 20 (FIG. 1C)essentially has the same quadrilateral shape as the mesa islands 18 inthe single crystal semiconductor donor layer, but with smallerdimensions. That is, the remaining dielectric layer material 20 (FIG.1C), which supports the mesa islands 18, may have essentially aquadrilateral shape, e.g., square, rectangle, rhombus, parallelogram,etc., when viewed from the top, and having smaller dimensions, therebyleaving floating or semi-floating mesa islands 18 formed in the SOIsubstrate 10.

In some embodiments, prior to deposition of the Group IIIA nitridelayer, the SOI substrate 10 comprising the pattern of mesa islands 18may be cleaned. For example, in some embodiments, the SOI substrate 10may be baked in a hydrogen atmosphere at a temperature between about900° C. and about 1100° C. These baking conditions may be suitable toclean residue trace oxide on the silicon device layer comprising themesa islands.

3. Deposition of Buffer Layer on Mesa Islands

In some embodiments, prior to deposition of the Group IIIA nitridelayer, a buffer layer may be optionally deposited on the pattern of mesaislands 18 formed in the single crystal semiconductor device layer ofthe SOI substrate 10. The buffer layer may comprise an aluminum nitridelayer formed on the pattern comprising the plurality of mesa islands 18.In some embodiments, an aluminum nitride layer may be deposited bymetalorganic chemical vapor phase deposition (MOCVD) or metalorganicvapor phase epitaxy (MOVPE), generally at a temperature between800-1100° C. Molecular beam epitaxy is also an option for AlNdeposition. Deposition instrumentation is available commercially frommanufacturers such as Aixtron and Vecco. The aluminum nitride layer maybe deposited to a thickness between about 1 nanometer and about 500nanometers, such as between about 10 nanometers and about 100nanometers. The buffer layer may comprise an aluminum gallium nitridelayer formed on the pattern comprising the plurality of mesa islands. Ingeneral, aluminum gallium nitride may be deposited by metalorganicchemical vapor phase deposition (MOCVD) or metalorganic vapor phaseepitaxy (MOVPE), generally at a temperature between 800-1100° C. Thealuminum gallium nitride layer may be deposited to a thickness betweenabout 1 nanometer and about 500 nanometers, such as between about 10nanometers and about 100 nanometers. In some embodiments, the bufferlayer may comprise an aluminum gallium nitride layer formed on analuminum nitride layer prior to forming the Group IIIA-nitride layer onthe pattern comprising the plurality of mesa islands.

4. Deposition of Group IIIA-Nitride Layer on Mesa Islands

With reference now to FIG. 1D, the SOI structure 10 comprising thesingle crystal semiconductor handle wafer 12, the remaining portion ofthe dielectric layer 20 comprising the supporting structures, and thepattern of semi-floating mesa islands 18 formed from the single crystalsemiconductor device layer supported by the remaining portion of thedielectric layer 20 is next subjected to deposition of a GroupIIIA-nitride layer 22. In the context of the present invention, GroupIIIA refers to the boron group of elements, including boron, aluminum,gallium, and indium. Accordingly, Group IIIA-nitrides include boronnitride, aluminum nitride, gallium nitride, and indium nitride. Inpreferred embodiments, gallium nitride is deposited on the pattern ofmesa islands. The gallium nitride may be deposited on a buffer layer,which was previously deposited upon the mesa islands. The GroupIIIA-nitride layer may be deposited using metalorganic chemical vapordeposition (MOCVD), metalorganic vapor phase epitaxy (MOVPE), ormolecular beam epitaxy (MBE). In some preferred embodiments, the GroupIIIA nitride layer may be deposited using metalorganic chemical vapordeposition (MOCVD). A suitable MOCVD reactor may be a Veeco TurboDisc oran Aixtron G5. Aluminum precursors suitable for MOCVD includetrimethylaluminum aind triethylaluminurn. Gallium precursors for MOCVDinclude trimethylgallium and triethylgalliumrn Indium precursorssuitable for MOCVD include trimethylindium, triethylindium,di-isopropylmethylindium, and ethyldimethylindium. Nitrogen precursorssuitable for MOCVD include Ammonium, phenyl hydrazine, dimethylhydrazine, tertiary butyl amine, and ammonia. Boron precursors includediborane, boron chloride, 1,3,5-tri(N-methyl)borazine. The molar ratioof Group V precursor (e.g., ammonia) to Group IIIA precursor (e.g.,trimethyl gallium) may be between 1 to 10000, preferably between 100 to1000. A MOCVD reactor comprises a chamber comprising reactor walls,liner, a susceptor, gas injection units, and temperature control units.The parts of the reactor are made of materials resistant to andnon-reactive with the precursor materials. To prevent overheating,cooling water may be flowing through the channels within the reactorwalls. A substrate sits on a susceptor which is at a controlledtemperature. The susceptor is made from a material resistant to themetalorganic compounds used, such as SiC or graphite. Reactive gas isintroduced by an inlet that controls the ratio of precursor reactants.Before GaN growth, a seed layer of AlN may be deposited to a thicknessbetween about 1 nanometer and about 200 nanometers, or between about 5nanometers and about 100 nanometers, or between about 50 nanometers andabout 100 nanometers, The growth temperature may be between about 600°C. and about 1200° C., such as between about 800° C. and about 1200° C.,preferably between about 1000° C. and about 1150° C. The Group IIIAnitride may be formed under reduced pressure, such as between about 10Torr to about 760 Torr (about 101 kPa), preferably between about 10 Torr(about 1.33 kPa) and about 80 Torr (about 10.67 kPa). Upon GaN growth,the diffusion of precursors from the gas phase to the cavities betweentwo adjacent mesa islands is retarded, which further suppresses thedeposition of nitride materials. The Group IIIA-nitride layer may bedeposited to a thickness between about 500 nanometers and about 200micrometers, such as between about 500 nanometers and about 100micrometers, or between about 1 micrometer and about 50 micrometers, orbetween about 2 micrometers and about 10 micrometers. The strain innitride layers is released by both misfit dislocations and the elasticdeformation of the semi-floating Si layer.

The Group IIIA-nitride layer deposited according to the method of thepresent invention may have a threading dislocation density between about10⁶/cm² and about 10⁹/cm², such as between about 10⁷/cm² and about10⁸/cm². In some embodiments of the present invention, the GroupIIIA-nitride layer may be deposited to a thickness such that thethreading dislocation density is less than about 10⁶/cm², such asbetween about 10³/cm² and about 10⁶/cm², or between about 10³/cm² andabout 10⁵/cm². The method of the present invention enables the growth ofthick GaN layers without cracking. It is known that threadingdislocation density (TDD) (Kapper, J C G, 300, 70 (2007) is dependentupon the thickness of the Group IIIA nitride layer. According to themethod of the present invention, thick GaN layers can be grown, leadingto reduced TDDs. However, GaN epi layer thickness from conventional GaNgrowth on blanket substrates is constrained by layer cracking due to CTE(coefficient of thermal expansion) mismatch between GaN and thesubstrate, which is generally below 5 um along with threadingdislocation density of about 10⁸/cm². The method of the presentinvention overcomes CTE constraints by GaN growth on mesa islands.Therefore, GaN layer thickness can be extended to 10 um and above, evenas thick as 100 micrometers or more, which leads to substantiallyreduced threading dislocation density.

Additional defect engineering can be applied to reduce the threadingdislocations, such as in-situ SiNx nanopatterning. See Kapper, J C G,300, 70 (2007) and U.S. Pat. No. 7,708,832B2. Nanopatterning involvesthe use of dielectrics (such as Si₃N₄) to block or terminate threadingdislocations on the growth front surface of GaN layer. As the dielectricis thin (˜1 nm), it has pinholes that provide access to the underlyingGaN epi layer in the subsequent epitaxial growth. Epitaxial lateralgrowth above the dielectric mask promotes the formation of a continuouslayer. See Kapper. The dielectric mask can be formed in the MOCVDreactor (in-situ) or by other deposition techniques, such as CVD, ALD,etc. The dielectric mask layer can be Si₃N₄, SiO₂, or other oxide.

5. Device Structures Manufactured in the Group IIIA-Nitride Layer

In some embodiments and with reference to FIG. 3A, upon completion ofdeposition of the Group IIIA-nitride layer 108 on the pattern of mesaislands 106 formed in the single crystal semiconductor device layer (16in FIG. 1A), multiple quantum wells and a P—GaN contact layer 110 can bedirectly grown to complete a LED device structure. The growth of quantumwells is discussed in the literature. See, e.g., Zhang, phys. stat. sol.(a) 188, No. 1, 151-154 (2001)]. After formation of quantum wells in theGroup IIIA-nitride layer, the structure 100 comprises the single crystalsemiconductor handle wafer 102, a layer of supporting structures 104derived from the dielectric layer (e.g., buried oxide layer, and 14 inFIG. 1A), a layer comprising the pattern of mesa islands 106 (derivedfrom the device layer 16 in FIG. 1A), the layer of Group IIIA-nitride108 formed on layer comprising the pattern of mesa islands 106, and themultiple quantum wells and P—GaN contact layer 110 formed in the layerof Group IIIA-nitride 108. In some embodiments, the mesa islands 106comprising the Group IIIA-nitride 108 and the quantum wells 110 aretransferred to another substrate, such as glass to complete LED devicefabrication and packaging.

In some embodiments and with reference to FIG. 3B, upon completion ofdeposition of the Group IIIA-nitride layer 108 on the pattern of mesaislands 106 formed in the single crystal semiconductor donor layer, alateral high-electron-mobility transistor (HEMT) device 120, 122 may bedirectly grown on the Group IIIA-nitride layer 108. The HEMT device maybe used as a power device or as a radiofrequency device. The die couldthen be detached and mounted directly into a package. The thin structure(thin silicon with heteroepi layers) would help minimize thermalconductivity losses. A lateral high-electron-mobility transistor (HEMT)device 140 that may be manufactured on a Group IIIA-nitride, e.g., GaNis illustrated in FIG. 4. See also, e.g., Joshin, Proceedings ofAsia-Pacific Microwave Conference, 2006. In the lateral HEMT device 140depicted in FIG. 4, electrons flow horizontally from source 142 to drain144 along the 2-dimensional electron gas 148 (2DEG) formed at theinterface between AlGaN layer 146 and the GaN layer 150. Gate 152voltage modulates the 2DEG 148 to open or close the current path. A highelectric field is built up between drain 144 and gate 152 and breakdownvoltage is usually limited by this electric field. The electron densityof the 2DEG 148 determines the on-resistance (R_(on)) and the drivecurrent. As the 2DEG 148 electron density (5-10×10¹²/cm²) is induced bypolarization effect, the residual stress from CTE mismatch can changethe device performance as well as device reliability. See Jocob Leachand Hadis Morkoc, Proceedings of the IEEE, 1127, V98, No. 7, July 2010.The present invention enables reduction in the residual stress from CTEmismatch and provides more stable device performance.

Another advantage of the present invention is that it provides theoption to transfer the high-quality Group IIIA nitride layer (e.g., aGaN layer deposited by epitaxial deposition) to another carriersubstrate that is engineered to cater for the device application. Forexample, an insulating or semi-insulating or high resistivity carriersubstrate, such as sapphire or polycrystalline AlN, is used for an HEMTradio frequency (RF) devices built in GaN layers to minimize the RF lossand signal distortion. HEMT RF devices comprise similar structures toHEMT power devices, but they operate at lower voltages. The RF HEMTstructure is a lateral one like the high voltage (600V) power device.Because voltage requirement is much lower (<100V) the GaN layer may notbe as thick as for a power device, but otherwise the layer structure andsequence is typically the same. These devices are built onsemi-insulating substrates to avoid substrate coupling in high frequencysignal, in the Nitronex GaN/Si(111) case high resistivity silicon (>1000ohm-cm). A highly conductive carrier substrate, such as diamond ordiamond coated Si, can be used for power HEMT devices to facilitateheating dissipation.

In some embodiments, the structure as depicted in FIG. 1D is suitablefor use as a starting point in the manufacture of high voltage powerdevices. In the manufacture of high voltage power devices, the mesaislands comprising the Group IIIA-nitride material (e.g., GaN) may betransferred to a carrier substrate for additional growth of the GroupIIIA-nitride material and subsequent device fabrication. In someembodiments, the carrier substrate has properties of high thermalconductivity and low electrical conductivity. In some embodiments, thecarrier substrate may comprise a high resistivity single crystalsemiconductor substrate, such as a high resistivity single crystalsilicon substrate, a polycrystalline silicon substrate, an aluminumnitride substrate, a sapphire substrate, a polycrystalline aluminumnitride substrate, a diamond substrate, a diamond coated silicon wafer,and the like. With reference now to FIGS. 5A through 5D, a multilayerstructure 200 is provided comprising a single crystal semiconductorhandle wafer 202, a layer of supporting structures 204 derived from thedielectric layer (e.g., buried oxide layer, and 14 in FIG. 1A), a layercomprising the pattern of mesa islands 206 (derived from the devicelayer 16 in FIG. 1A), and the layer of Group IIIA-nitride 208 formed onlayer comprising the pattern of mesa islands 206.

In some embodiments, a thin interfacial bonding layer 210 is depositedon the layer of Group IIIA-nitride 208. In some embodiments, the thininterfacial bonding layer 210 comprises between about 1 nanometer andabout 5 nanometers of aluminum oxide (Al₂O₃). The interfacial bondinglayer 210 may be deposited by atomic layer deposition or molecular beamepitaxy.

After deposition of the interfacial bonding layer 210, the layer may beactivated for bonding by oxygen or nitrogen plasma activation. In someembodiments, the oxygen plasma surface activation tool is a commerciallyavailable tool, such as those available from EV Group, such as EVG®810LTLow Temp Plasma Activation System. The optionally cleaned single crystalsemiconductor donor wafer is loaded into the chamber. The chamber isevacuated and backfilled with O₂ to a pressure less than atmospheric tothereby create the plasma. The SOI multilayer structure 200 is exposedto this plasma for the desired time, which may range from about 1 secondto about 120 seconds. Oxygen plasma surface oxidation is performed inorder to render the front surface of the interfacial bonding layer 210hydrophilic and amenable to bonding to a single crystal semiconductorhandle substrate prepared according to the method described above.

With reference now to FIG. 5B, the multilayer structure 200 comprising asingle crystal semiconductor handle wafer 202, a layer of supportingstructures 204 derived from the dielectric layer (e.g., buried oxidelayer, 14 in FIG. 1A), a layer comprising the pattern of mesa islands206 (derived from the device layer 16 in FIG. 1A), and the layer ofGroup IIIA-nitride 208 formed on layer comprising the pattern of mesaislands 206, and the activated interfacial bonding layer 210 is nextbonded to a handle or carrier substrate 220. The handle or carriersubstrate 220 can be any substrate that is suitable for a specificapplication. For power HEMT devices, good thermal conductivitysubstrates, such as diamond are suitable. For vertical power devices,metal substrates, such as copper, are suitable substrates. For LEDdevices, a transparent substrate, such as sapphire and glass, aresuitable. For RF HEMT devices, semi-insulating or insulating substratesare preferred, such as sapphire, high-resistivity Si, AlN, etc. The bondbetween the multilayer structure 200 and the carrier substrate 220 isnot required to be strong. In some embodiments, the handle substrate 220only provides support to the GaN mesa island. In some embodiments, thereis no subsequent debonding process involved, such as cleaving. In someembodiments, the interface layer is optional provided that the plasmaactivation aided bonding process is used.

According to the process of the present invention, the dielectric layer204 is etched away to remove the dielectric layer and the single crystalsilicon handle substrate 202. In some embodiments, the dielectric layeris etched by immersing the bonded structure in an etchant solutioncomprising 1-10% HF. Once the remaining dielectric layer is completedetched, the pattern of mesa islands 206 and the layer of GroupIIIA-nitride 208 are released from the single crystal silicon handlesubstrate 202 substrate and are transferred to the carrier substrate220. At the interface of the Group IIIA-nitride layer 208 and thecarrier substrate 220, the interfacial bonding layer 210 is partiallyetched and weakens the bonding strength, which accommodates anypotential thermal stress in the subsequent Group IIIA-nitride thickeningprocess.

According to the process of the present invention, the mesa islandsformed in the single crystal semiconductor donor layer 206 are nextremoved to thereby prepare the structure 230 shown in FIG. 5C comprisingcarrier substrate 220, the interfacial bonding layer 210, and the GroupIIIA-nitride layer 208. This layer transfer process on a differentsubstrate provides versatile options for different device application.On the as-transferred GaN mesa islands, LEDs, a HEMT power device, and aHEMT radiofrequency device can be built. The mesa islands formed in thesingle crystal semiconductor donor layer 206 may be etched away byeither wet chemistry such as HNO₃/HF solution and TMAH or by plasmaetch. In some embodiments wherein buffer layers comprising AlN and/orAlGaN are present, a plasma etch is preferred. Plasma etch is alsosuitable for removing defective Group IIIA-nitride layers. Afterremoving the top defective layers, a high-quality Group IIIA-nitridelayer 208 (e.g., GaN) with threading dislocations between about 10⁶/cm²and about 10⁹/cm², such as between about 10⁷/cm² and about 10⁸/cm², isleft on the carrier substrate 220.

In some embodiments and with Reference to FIG. 5D, the high-qualityGroup IIIA-nitride layer 208 (e.g., GaN) may be thickened. In someembodiments, the high-quality Group IIIA-nitride layer 208 (e.g., GaN)may be thickened by epitaxial deposition, e.g., metalorganic vapor phaseepitaxy (MOVPE) or hydride vapor phase epitaxy (HVPE). Commerciallyavailable HVPE reactors include the Aura HVPE system from AgnitronTechnology, Inc. The Ga precursors can be synthesized GaN powder or Galiquid. HCl vapor gas is used to convert GaN or Ga liquid into GaClprecursor. NH₃ is used as the nitrogen precursor. Ar is used as thecarrier gas. GaN growth occur at a temperature between about 1000° C.and about 1200° C., typically from about 1000° C. to about 1100° C. Thegrowth rate can be as high as 100 micrometers per hour. In someembodiments, the Group IIIA-nitride layer can be thickened to athickness between about 2 micrometers and about 50 micrometers,preferably between about 5 micrometers and about 10 micrometers. In someembodiments, the Group IIIA-nitride layer can be thickened to athickness between about 2 micrometers and about 2000 micrometers, suchas between about 2 micrometers and about 1000 micrometers, or betweenabout 100 micrometers and about 300 micrometers.

In some embodiments, the thickened Group IIIA nitride layer, e.g., GaNlayer, may be doped during the growth process. In some embodiments, theGroup IIIA-nitride layer may be doped with an N type dopant, such assilicon Si, germanium Ge, sulfur S, selenium Se, and tin Sn. Suitableprecursors that may be incorporated into the gas recipe during layergrowth in order to dope the layer with an N type dopant may includeSiH₄, GeH₄, H₂S, H₂Se, and (C₂H₅)Sn. In some embodiments, the GroupIIIA-nitride layer may be doped with a P type dopant, such as Mg or Zn.Suitable precursors that may be incorporated into the gas recipe duringlayer growth in order to dope the layer with an N type dopant mayinclude Magnesium bis(cyclopentadienyl), diethyl zinc, and dimethylzinc. In some embodiments, the thickened Group IIIA nitride layer, e.g.,GaN layer, can be doped with silicon. In some embodiments, SiH₄ gas maybe added to the gas recipe during the Group IIIA-nitride layerthickening process in order to dope the layer with Si. In someembodiments, SiH₄ gas may be added during GaN layer thickening in orderto dope the GaN layer with Si. The inclusion of SiH₄ during GroupIIIA-nitride layer thickening may result in doping the layer with Si tothereby prepare n type Group IIIA-nitride layer. The inclusion of SiH₄during GaN layer thickening may result in doping the layer with Si tothereby prepare N type GaN layer. The dopant concentration may rangefrom about 1×10¹⁵ dopant atoms/cm³ to about 5×10²⁰ dopant atoms/cm³. Insome embodiments to prepare N− Group IIIA-nitride layers, theconcentration of Si dopant may range from about 1×10¹⁵ dopant atoms/cm³to about 3×10¹⁷ dopant atoms/cm³, such as from about 1×10¹⁶ dopantatoms/cm³ to about 3×10¹⁶ dopant atoms/cm³. In some embodiments toprepare N+ Group IIIA-nitride layers, the concentration of Si dopant mayrange from about 1×10¹⁸ dopant atoms/cm³ to about 5×10²⁰ dopantatoms/cm³, such as from about 1×10¹⁹ dopant atoms/cm³ to about 3×10²⁰dopant atoms/cm³. In some embodiments, e.g., embodiments wherein theGroup IIIA-nitride layer's intended use is for a vertical galliumnitride-on-gallium nitride high voltage power devices, the dopant levelmay be varied during the growth of the thickened Group IIIA-nitridelayer. Varying the dopant level enables the growth of Group IIIA-nitridelayer having multiple layers of different dopant concentration. In someembodiments, the Group IIIA-nitride layer may first be doped with N−dopant, such as Si, to a dopant level from about 1×10¹⁵ dopant atoms/cm³to about 3×10¹⁷ dopant atoms/cm³, such as from about 1×10¹⁶ dopantatoms/cm³ to about 3×10¹⁶ dopant atoms/cm³, which is followed by theformation of an N+ layer by increasing the dopant level to between about1×10¹⁸ dopant atoms/cm³ to about 5×10²⁰ dopant atoms/cm³, such as fromabout 1×10¹⁹ dopant atoms/cm³ to about 3×10²⁰ dopant atoms/cm³.

Multilayer structures 230 comprising the carrier substrate 220, theinterfacial bonding layer 210, and the thickened Group IIIA-nitridelayer 208, as depicted in FIG. 5D, are suitable for the fabrication ofHEMT power devices with target application of 800-1000V. The structuresare also suitable for HEMT RF devices, LEDs, laser diodes, and verticalgallium nitride-on-gallium nitride high voltage power devices, amongother uses.

In some embodiments, multilayer structures 230 comprising carriersubstrate 220, the interfacial bonding layer 210, and the thickenedGroup IIIA-nitride layer 208, as depicted in FIG. 5D, can also besubject to additional growth by epitaxy, e.g., hydride vapor phaseepitaxy (HVPE), to reach a target thickness of at least about 50micrometers, such as between about 50 micrometers and about 2000micrometers, or between about 50 micrometers and about 1000 micrometers,such as between about 100 micrometers and about 500 micrometers.Thickened Group IIIA-nitride layers may be achieved with reducedthreading dislocation density. In some embodiments, the GroupIIIA-nitride layers having a thickness between about 50 micrometers andabout 2000 micrometers, such as between about 100 micrometers and about1000 micrometers may have threading dislocation less than about 10⁶/cm²,such as between about 10³/cm² and about 10⁶/cm², or between about10³/cm² and about 10⁵/cm², which is compared to bulk GaN materials. Suchstructures 230 are suitable for use in the manufacture of vertical powerdevices (e.g., HEMT power devices) and laser diodes as well as highbrightness LEDs. See, e.g., Uesugi, CS MANTECH Conference, Florida,2009. A vertical power device is suitable for handling high power, suchas 20 kW and above. The structures 230 depicted in FIG. 5D are alsosuitable for vertical gallium nitride-on-gallium nitride high voltagepower devices. See, e.g., Kizilyalli et al., Vertical Devices in BulkGaN Drive Diode Performance to Near-Theoretical Limits, HOW2POWER TODAY,March 2013. The advantage of vertical power device over lateral HEMTdevice is: smaller size, higher breakdown voltage and lower parasiticinductance. However, since the current flow thru the whole GaN layer,the requirements for GaN quality, like threading dislocations andimpurities are more stringent. So far, vertical power device is made onsmall size bulk GaN substrates that are expensive. In this disclosure,with the GaN growth on floating and semi-floating mesa islands, a viableapproach is provided to grow thick GaN materials that have comparablephysical and electrical properties of bulk GaN substrates at a lowercost. The disclosed method uses conventional growth method, MOCVD orMOVPE and is manufacturing scalable on large substrates.

The present invention therefor provides high quality thick GroupIIIA-nitride layers, suitably GaN layers, without cracks. The GroupIIIA-nitride layers can be deposited to thicknesses of at least 500nanometers, and can be grown up to 1000 micrometers thick. The method ofthe present invention minimizes residual stress in GaN layer, therebyreducing the impact of stress on device performance. The technique issuitably scaled to large wafer size up to 200 mm and beyond. The methodof the present invention provides layer transfer options. Eliminates thepotential harm on RF and power device from the conductive layer betweenthe AlN seed layer and the Si substrate due to the autodoping of Al inSi. The method of the present invention enables the integration ofoptoelectronic device with CMOS devices on Si substrates. The method ofthe present invention improves GaN quality to boost the performance ofLED, RF, Power devices.

Having described the invention in detail, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims.

As various changes could be made in the above compositions and processeswithout departing from the scope of the invention, it is intended thatall matter contained in the above description be interpreted asillustrative and not in a limiting sense.

When introducing elements of the present invention or the preferredembodiment(s) thereof, the articles “a,” “an,” “the,” and “said” areintended to mean that there are one or more of the elements. The terms“comprising,” “including,” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

What is claimed is:
 1. A multilayer structure comprising: a carriersubstrate; an interfacial bonding layer; and a Group IIIA-nitride layer,the Group IIIA-nitride layer having a thickness between about 500nanometers and about 2000 micrometers.
 2. The multilayer structure ofclaim 1 wherein the Group IIIA-nitride layer has a thickness betweenabout 500 nanometers and about 100 micrometers.
 3. The multilayerstructure of claim 1 wherein the Group IIIA-nitride layer has athickness between about 2 micrometers and about 10 micrometers.
 4. Themultilayer structure of claim 1 comprising threading dislocations at athreading dislocation density between about 10⁶/cm² and about 10⁹/cm².5. The multilayer structure of claim 1 comprising threading dislocationsat a threading dislocation density between about 10⁷/cm² and about10⁸/cm².
 6. The multilayer structure of claim 1 wherein the GroupIIIA-nitride layer has a thickness between about 100 micrometers andabout 1000 micrometers.
 7. The multilayer structure of claim 1 whereinthe Group IIIA-nitride layer has a thickness between about 100micrometers and about 300 micrometers.
 8. The multilayer structure ofclaim 1 comprising threading dislocations at a threading dislocationdensity less than about 10⁶/cm².
 9. The multilayer structure of claim 1comprising threading dislocations at a threading dislocation densitybetween about 10³/cm² and about 10⁵/cm².
 10. The multilayer structure ofclaim 1 wherein the carrier substrate is selected from the groupconsisting of sapphire and polycrystalline aluminum nitride.
 11. Themultilayer structure of claim 1 wherein the carrier substrate isselected from the group consisting of diamond and diamond coatedsilicon.
 12. The multilayer structure of claim 1 further comprisingquantum wells formed in the Group IIIA-nitride layer and a P—GaN contactlayer.
 13. The multilayer structure of claim 1 further comprisingcomponents of a lateral HEMT power device.
 14. The multilayer structureof claim 1 further comprising components of a lateral HEMTradiofrequency device.
 15. The multilayer structure of claim 1 furthercomprising components of a light emitting diode.
 16. The multilayerstructure of claim 1 further comprising components of a laser diode. 17.The multilayer structure of claim 1 further comprising components of avertical gallium nitride-on-gallium nitride high voltage power device.